Epilepsy is a common chronic condition disproportionately affecting children and which is often caused by brain insults which elevate extracellular neurotransmitter levels. My long-term goal is to elucidate fundamental pathological processes produced by such injuries in order to better understand the process of epileptogenesis and intervene with novel therapies. To this end, I have developed a new in vitro model which mimics such an initial insult and which produces persistent epileptiform discharges. In the proposed set of experiments I will test the hypothesis that persistent hyperexcitability in this new model is due to decreased release of GABA by inhibitory interneurons. This hypothesis is based on my observations that: 1) the model produces persistent epileptiform discharges, 2) spontaneous inhibitory post-synaptic current (sIPSC) frequency is decreased compared to controls, and 3) sIPSC amplitude and decay kinetics are unaffected. Given these observations, I propose experiments which focus on pre-synaptic inhibitory mechanisms, as well as key alternative hypotheses. Using my model of early post-natal hyperexcitability, four specific aims will be addressed: 1) Characterize pre-synaptic inhibitory function. I will assess frequency, amplitude, and decay kinetics of sIPSCs, miniature IPSCs, and evoked IPSCs as well as GABA release probability. I will also determine expression levels of enzymes vital to pre-synaptic synthesis and packaging of GABA. 2) Characterize pre-synaptic excitatory function. I will determine glutamate release probability and assess miniature excitatory post-synaptic current frequency, amplitude, and decay kinetics. I will also determine expression levels of the enzyme responsible for pre-synaptic packaging of glutamate. 3) Characterize principal cell intrinsic properties and cell number. I will assess principal cell intrinsic properties using whole cell recording and count principal cells using quantitative stereology. 4) Characterize inhibitory interneuron intrinsic properties and cell number. I will assess I will assess inhibitory interneuron intrinsic properties using whole cell recording and count interneurons using quantitative stereology. expect that these experiments will lead to translational research which improves treatment of children with epilepsy.